Both legislative and marketplace developments are pushing for reduced volatile organic emissions in a variety of industries. In an increasing number of industries, aqueous coating compositions continue to replace solvent-based compositions in efforts to reduce volatile organic emissions. A variety of paints, inks, sealants, and adhesives which were previously formulated with organic solvents are now formulated as aqueous compositions. However, conventional resins used for these compositions are mostly hydrophobic, and thus it is difficult to disperse them with water or otherwise make such resins compatible with water. Further, it is generally known that crystalline polyesters are not dispersible in or compatible with water.
U.S. Pat. No. 2,976,266 describes film-forming copolyesters based on combinations of 4,4'-biphenyl dicarboxylic acid (BDA) with linear and branched aliphatic glycols. U.S. Pat. Nos. 3,842,040 and 3,842,041 describe manufacturing processes where poly(ethylene-4,4'-biphenyl dicarboxylate) may be prepared from ethylene oxide or ethylene glycol and BDA. A number of patents describe copolyesters comprised of BDA and their blends with a large group of property modifiers. (See, for example, U.S. Pat. Nos. 5,011,877 and 5,037,947). These references describe narrow compositional ranges for copolyesters of BDA with various combinations of cycloaliphatic and aliphatic glycols, none of which provided water-dispersible polyesters. In fact, excellent solvent resistance is cited in a number of the examples. Water is specifically identified as having no effect on molded bars after 24 hours in U.S. Pat. Nos. 5,011,877 and 5,037,947.
Linear, water-dispersible polyesters and polyesteramides, based on the incorporation of sulfonate groups were first reported in U.S. Pat. Nos. 3,734,874 and 3,779,993. These references taught a number of dicarboxylic acids as potential components of these polyesters, and included diphenic acid: ##STR1## However, neither reference taught the use of BDA.
Further examples of water-dispersible sulfopolyester compositions can be found in U.S. Pat. Nos. 5,290,631 and 4,233,196.
U.S. Pat. No. 4,483,976 describes various polyester binder fibers and lists dicarboxylic acid components that include both biphenyl dicarboxylic acid and diphenic acid; however, the 4,4' isomer is not specifically disclosed. Further, the specification teaches only compositions containing from about 5-20 mole % of a low to medium molecular weight poly(ethylene glycol). U.S. Pat. No. 4,699,845 teaches certain adhesive polyester films and lists biphenyl dicarboxylic acid without specifying viability of a particular isomer, although specific isomers of phthalic and naphthalene dicarboxylic acid are indicated for this end use. Further, the invention is limited to compositions containing at least 60 mole % on an aromatic dicarboxylic acid and less than 60 mole % of diethylene or triethylene glycol. Also noted was a dispersion concentration of 1-8% by weight.
None of the cited references describe copolyesters containing residues of 4,4'-biphenyl dicarboxylic acid which have excellent water-dispersibility. There is also no mention in the above references of compositions having substantial amounts of crystallinity and the concomitant benefits thereof. It is generally known in the art that crystalline polyesters tend to possess excellent water-resistance; thus, it is surprising that the polymers of the present invention, as described below, retain the desired properties of water-dispersibility as well as possessing substantial amounts of crystallinity.